Curl resistant foil to paper lamination and method of making same



July 23, 1963 J. N. KRAUSE CURL RESISTANT FOIL TO PAPER LAMINATION ANDMETHOD OF MAKING SAME Filed Aug. 4, 1958 INVENTOR James [\[Krause UniteThis invention relates to metallic foil to paper lamination andprocesses for producing such laminations, and more particularly to foilto paper laminations which are treated during their manufacture toreduce the tendency of the lamination to curl due to changes in relativehumidity in the surrounding atmosphere.

The invention is especially directed toward the production of alamination consisting of a layer of aluminum fioil which is bonded to apaper backing. Laminations of this type are widely used for labelsapplied to bottles or packages. During the normal process ofmanufacturing such labels, the drying of the bonding media also dries orshrinks the paper backing. When the lamination is exposed to theatmosphere, as during storage, the paper picks up moisture from theatmosphere and swells. Since the aluminum foil member of the laminationis dimensionally stable to varying moisture conditions, swelling of thepaper backing causes the lamination to curl with the foil on the insideof the curl. If the lamination is not properly dried or left too wet,then it gives off moisture to the atmosphere and the paper membershrinks. This causes the lamination to curl in the opposite direction.This problem is particularly acute where the labels are prepared for usein automatic labeling machinery by cutting the labels to size andstoring them in stacks.

Previously, the general practice in the industry has been to dry thecompleted lamination to a point where the moisture content of the paperbacking is between 3 and 4 percent of the weight of the paper backing.This practice has been followed to avoid possible corrosive effects tothe foil due to the presence of moisture in the paper. A paper backinghaving a moisture content of between 3 and 4 percent is in moistureequilibrium with the surrounding atmosphere at relative humidities inthe range of approximately to percent. Since this particular range ofrelative humidity is abnormally low, it is apparent that foil to paperlaminations are extremely susceptible to swelling by taking up waterfrom the atmosphere when the l-aminations are exposed to relativehumidities which ordinarily vary from between 30 to 80 or 90 percent.The swelling of the paper causes the lamination to curl,

as described above, thus rendering the lamination difficult to handle,and in many cases making the lamination unsuitable for use in labelingmachines or other types of equipment.

A primary object of my invention is to provide a foil to paperlamination which is resistant to curling over a wide range of relativehumidity in the surrounding atmosphere.

Another object of my invention is to provide a method for producing afoil to paper lamination which is resistant to curling over a wide rangeof relative humidity in the surrounding atmosphere.

Other objects and advantages of the invention will become apparent byreference to the following specification taken in conjunction with theaccompanying drawings.

In the drawings:

FIG. 1 is a schematic showing of an apparatus for producing a laminationin accordance with the invention; and

FIG. 2 is an enlarged view of a portion of the apparatus of FIG. 1.

In the drawings, one arrangement for producing a curl 3,098,780 PatentedJuly 23, 1963 ice resistant foil to paper lamination according to theinvention includes a supply roll of metallic foil 10 from which acontinuous strip of metallic foil is fed to a bonding materialapplicator station 12. Foil from supply roll 10 is trained over an upperroll 14 at station 12, roll 14 being in rolling contact with a lowerroll 16 which is partially submerged in a tank 18- oontaining thebonding material. Bonding material from the tank 18 is trans ferred fromthe surface of lower roll 16 to the surface of upper roll 14- from whichit is applied to the lower surface of the metallic foil sheet.

Coated foil from station 12 and a continuous strip of paper from a papersupply roll 24 are fed between upper and lower pressing rolls 20 and 22.As the foil and paper strips pass between rolls 2t) and 22, they arepressed into firm engagement with each other by the pressing rolls andthe bonding material applied to the foil at station 12 bonds the paperand foil into a lamination.

The lamination is fed from the pressing rolls to a treating station 25at which the lamination passes between upper and lower rolls 26 and 28respectively. Lower roll 28 is formed with a surface of a resilientmaterial such as rubber and is mounted to rotate partially submergedwithin a bath 30 of treating solution. Upper roll 26 is constructed fromsteel and is located to exert a cushioned squeezing action on thelamination by pressing the lamination firmly against the rubber surfaceof roll 28.

Rotation of roll 28 in the indicated direction carries treating liquidupwardly into contact with the lower or exposed surface of the paper. Tocompletely flood the exposed surfiace of the paper with treatingsolution, a blade 32 extends beneath the path of the lamination to actas a dam which maintains a substantial supply of treating solution inposition to be contacted by the paper as it passes between rolls 26 and28 by trapping treating solution squeezed from the paper as thelamination passes between rolls 26 and 28.

From the treating station, the lamination is passed through a dryingchamber 34 and from drying chamber 34- to a take-up roll 36.

An important feature of the process resides in regulating the moisturecontent of the paper as it passes on to take-up roll 36. To measure themoisture content, an electronic moisture meter 38 is located to measurethe moisture content of the paper as it passes from the drying chamberto the take-up roll. Suitable meters of this type are commerciallyavailable; one well-known type measures the moisture content bymeasuring the electrical resistance through the lamination, theelectrical resistance varying with the amount of moisture in the paper.

In accordance with this invention, the moisture content of the papershould be between 5% and 7% of the weight of the paper as the laminationis passed from drying chamber 34 to take-up roll 36. The moisturecontent of the paper at this point may be adjusted by observing themoisture content measured by meter 38 and regulating the speed at whichthe lamination is moved through drying chamber 34 or by adjusting thetemperature within chamber 34.

The composition of treating solution applied to the paper isdeter-mined, at least in part, by the use to which the lamination is tobe put. Basically, the treating solution is applied for the purpose ofreducing the ability of the paper to take up moisture. Many agents forthis purpose are commercially available.

Treating solutions which are suitable for use in the above-describedprocess may be divided generally into three types: stabilizers, sizers,and humectants. Each of the three diiferent types of treating agentsacts to prevent the paper from taking up moisture in a slightlydifferent manner. In a simplified manner, the actions of the respective.agents may be distinguished by stating that in general stabilizerschemically combine with the paper in a manner which reduces the volumeof space within the paper :where moisture may be received. Sizers act toform a Water resistant coating on the surface of the paper and thusprevent moisture from penetrating into the paper. Humectants in generalact to attract the moisture to themselves and prevent the moisture fromsoaking into: the paper fibers.

In general, a foil to paper lamination having satisfactory curlresistant tendencies may be manufactured by a process which includestreatment with an agent falling into any one of the above types. Thetype of agent eventual-ly selected is one whose effects, aside from itsmoisture control characteristics, on the finished product are ofinterest. For example, many sizers impart a certain stiffness orrigidity to the finished product. This property is often desirable whererelatively thin or light weight paper stock is employed. Thus, assumingthat agents of each of the three different types mentioned above ofequal effectiveness in reducing the ability of the particular paper inquestion to take up water were available, the sizing agent would bechosen where stiffness or rigidity in the finished product wasdesirable. If stiffness is undesira'ble in the finished product, thehumcct-ant type agent would probably be chosen.

In order to obtain optimum curl resistant characteristics in thecompleted lamination, it is necessary to adjust or regulate the moisturecontent of the paper to tall within the range of between and 7% of theweight of the paper at the completion of its manufacture. Thisparticular range is a departure from previous practice in which thecompleted lamination is conventionally dried to a moisture content ofbetween 3 and 4 percent of the Weight of the paper. A final moisturecon-tent of between 3 and 4 percent has been previously thoughtdesirable in order to assure against possible corrosive eflects to themetallic foil because of the presence of the moisture in the paper.Experience 'has proven that the possibility of corrosion is notincreased by any practical extent at rnoisture contents of between 5%and 7% It has been found desirable to achieve .a moisture content of atleast 5% in the finished lamination since the tendency of the completedlamination to curl increases at moisture contents below 5%.

Since the treating agent is usually applied in the form.

of a water solution the final moisture content of the paper is easilyachieved by drying the lamination after the treating solution has beenapplied to the paper.

The following examples represent typical practices of the process.

(1) Paper stock bonded to a thin aluminum foil was treated in the mannerdescribed above with a 10% sugar solution. The treated lamination wasdried to a moisture content of 6% and subsequently exhibitedsatisfactory curl resistant properties when exposed to various humidityconditions.

(2) Paper stock bonded to thin aluminum foil was treated in the mannerdescribed above with a 5% Stab-U- Cel solution. Stab-U-Cel is an organicester manufactured by the Upson Chemical Corporation. After treatment,the lamination was dried to a final moisture content of 6%. Label stockcut from the treated lamination exhibited satisfactory curl resistantproperties when tested over relative humidities ranging from 30 to Thecurl resistant properties were slightly improved over those obtained inExample 1 above.

(3) Paper stock bonded to: thin aluminum foil was treated With a 1%Aqu-apel solution. Aquapel is manufactured by the Hercules PowderCompany and is composed of approximately equal parts of stearic acid andpalmitic' acid to which an emulsifying agent is added. After treatmentthe lamination was dried to a moisture content of 6%. Labels out fromthis stock exhibited satisfactory curl resistant properties slightlyimproved over those obtained in Example 2 above when exposed to similarhumidities.

It should be emphasized that the foregoing examples are merelyrepresentative. Basically, the achievement of a metallic foil to paperlamination having satisfactory curl resistant characteristics isdependent upon the combination of a treatment which reduces ability ofthe paper to take up moisture combined with a subsequent adjustment ofthe moisture content of the paper to achieve a moisture content ofbetween 5% and 7% of the weight of the paper, the optimum moisturecontent being 6%.

The foregoing description is to be considered exemplary rather thanlimiting, and the true scope of my invention is that defined in thefollowing claims.

I claim:

1. The method of making a foil to paper lamination for use as a label orsimilar article having improved curl resistant properties when stored instacks comprising the steps of bonding the paper to the foil, treatingthe exposed suiface of the paper to reduce the ability of the paper totake up moisture, and subsequently adjusting the moisture content of thepaper to between 5 and 7% of the Weight of the paper.

2. The method of making a toil to paper lamination for use as a label orsimilar article having improved curl resistant properties when stored instacks comprising the steps of bonding the paper to the foil, treatingthe exposed surface of the paper with a solution containing a treatingagent operable to reduce the ability of the paper to take up moisture,and subsequently drying the lamination to reduce the moisture content ofthe paper to between 5 and 7% of the weight of the paper.

3. The method of making a foil to paper lamination for use as a label orsimilar article having improved curl resistant properties when stored instacks comprising the steps of bonding the paper to the foil, treatingthe exposed surface of the paper with a solution containing a treatingagent operable to reduce the ability of the paper to take up moisture,and subsequently drying the lamination to reduce the moisture content ofthe paper to sub stantially 6% of the Weight of the paper.

References Cited in the file of this patent UNITED STATES PATENTS1,719,607 Harvey July 2, 1929 2,321,258 Stamm et a1 June 8, 19432,544,146 Erikson Mar. 6, 1951 2,778,760 Hurst Jan. 22, 1957

3. THE METHOD OF MAKING A FOIL TO PAPER LAMINATION FOR USE AS A LABEL ORSIMILAR ARTICLE HAVING IMPROVED CURL RESISTANT PROPERTIES WHEN STORED INSTACKS COMPRISING THE STEPS OF BONDING THE PAPER TO THE FOIL, TREATINGTHE EXPOSED SURFACE OF THE PAPER WITH A SOLUTION CONTAINING A TREATINGAGENT OPERABLE TO REDUCE THE ABILITY OF THE PAPER TO TAKE UP MOISTURE,AND SUBSEQUENTLY DRYING THE LAMINATION TO REDUCE THE MOISTURE CONTENT OFTHE PAPER TO SUBSTANTIALLY 6% OF THE WEIGHT OF THE PAPER.